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Love letter for the Lanius
(hexbear.net)
These little guys are the best crewmates possible in FTL. Not only do they not need oxygen making it safe to repair breaches, but they DRAIN oxygen from the room they're in, meaning fire is virtually powerless against them, and any enemies that decide to fight them will most likely suffocate to death in the process, making their combat viability comparable to a mantis.
By far my favorite crewmates in vanilla.
I was mostly referring to vanilla. You throw multiverse into the mix and things get more... complicated.
Oh gotcha, I didn't play vanilla for very long.